303-guruh talabasi Raxmanova Ayshaning Simsiz tarmoqlar fanidan 1-mustaqil ishi

Contents

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  1Analog modulation methods
  
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  2Digital modulation methods
  
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    2.1Fundamental digital modulation methods
    
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    2.2Modulator and detector principles of operation
    
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    2.3List of common digital modulation techniques
    
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    2.4Automatic digital modulation recognition (ADMR)
    
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    2.5Digital baseband modulation or line coding
    
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  3Pulse modulation methods
  
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  4Miscellaneous modulation techniques
  
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  5See also
  
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  6References
  
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  7Further reading
  
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  8External links
  

Analog modulation methods[edit]

A low-frequency message signal (top) may be carried by an AM or FM radio wave.

Waterfall plot of a 146.52 MHz radio carrier, with amplitude modulation by a 1,000 Hz sinusoid. Two strong sidebands at + and - 1 kHz from the carrier frequency are shown.

A carrier, frequency modulated by a 1,000 Hz sinusoid. The modulation index has been adjusted to around 2.4, so the carrier frequency has small amplitude. Several strong sidebands are apparent; in principle an infinite number are produced in FM but the higher-order sidebands are of negligible magnitude.
In analog modulation, the modulation is applied continuously in response to the analog information signal. Common analog modulation techniques include:

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  Amplitude modulation (AM) (here the amplitude of the carrier signal is varied in accordance with the instantaneous amplitude of the modulating signal)
  
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    Double-sideband modulation (DSB)
    
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      Double-sideband modulation with carrier (DSB-WC) (used on the AM radio broadcasting band)
      
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      Double-sideband suppressed-carrier transmission (DSB-SC)
      
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      Double-sideband reduced carrier transmission (DSB-RC)
      
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    Single-sideband modulation (SSB, or SSB-AM)
    
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      Single-sideband modulation with carrier (SSB-WC)
      
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      Single-sideband modulation suppressed carrier modulation (SSB-SC)
      
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    Vestigial sideband modulation (VSB, or VSB-AM)
    
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    Quadrature amplitude modulation (QAM)
    
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  Angle modulation, which is approximately constant envelope
  
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    Frequency modulation (FM) (here the frequency of the carrier signal is varied in accordance with the instantaneous amplitude of the modulating signal)
    
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    Phase modulation (PM) (here the phase shift of the carrier signal is varied in accordance with the instantaneous amplitude of the modulating signal)
    
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    Transpositional Modulation (TM), in which the waveform inflection is modified resulting in a signal where each quarter cycle is transposed in the modulation process. TM is a pseudo-analog modulation (AM). Where an AM carrier also carries a phase variable phase f(ǿ). TM is f(AM,ǿ)
    

Digital modulation methods
In digital modulation, an analog carrier signal is modulated by a discrete signal. Digital modulation methods can be considered as digital-to-analog conversion and the corresponding demodulation or detection as analog-to-digital conversion. The changes in the carrier signal are chosen from a finite number of M alternative symbols (the modulation alphabet).

Schematic of 4 baud, 8 bit/s data link containing arbitrarily chosen values